The present invention relates to friction clutches for motor vehicles and in particular for use in cars and motorcycles, more particularly racing cars and motorcycles.
The type of friction clutches used in racing cars and motorcycles are such that clutch travel between a clutch release position and a clutch engaged position is very small. This in effect means that clutch engagement is very sudden and sharp.
It is known to reduce the sudden engagement of a clutch by providing cushioning in the force path between the clutch engagement spring means and the flywheel or reaction plate of the clutch. For example the applicant""s prior patent WO 93/07400 discloses a friction clutch for a motor vehicle in which an annular plate coaxial and rotationally fast with the flywheel is biased away from the flywheel to provide axial cushioning of the clutch engagement.
The present invention seeks to further improve such friction clutches.
It is also and objective of the present invention to provide an axially cushioned clutch which is simpler and cheaper to produce than prior art axially cushioned clutches.
It is a further objective to provide and axially cushioned clutch in which the cushioning characteristics can be set or adjusted more reliably and/or more quickly than with the known axially cushioned clutches.
According to a first aspect of the invention there is provided a friction clutch having means to cushion engagement of the clutch, the cushioning means comprising at least one resilient means arranged in a recesses in a first component of the clutch, the at least one resilient means acting to bias a second component of the clutch away from the first component to provide the cushioning, characterised in that the or each resilient means is arranged to act on the second component via an insert mounted in a recess in the second component.
The first aspect of the invention provides a cushioned clutch which is axially compact since the resilient means is located in a recess in the first component and the insert is located in a recess in the second component. The invention provides a particularly compact arrangement when applied to a multi-plate clutch in which the second component is one of the drive plates. More particularly, the invention may be applied to a multi-plate clutch in which the drive and driven plates are made from a carbon/carbon matrix material in which direct contact between the resilient means and one of the driven plates would be liable to result in the driven plate being damaged. The use in these circumstances of an insert arranged in a recess in the driven plate provides a means of preventing direct contact between the resilient means and the drive plate without increasing or only minimally increasing the overall axial dimensions of the clutch.
According to a second aspect of the invention there is provided a friction clutch having means to cushion engagement of the clutch, the cushioning means comprising a plurality of circumferentially spaced resilient means arranged in one or more recesses in a first component of the clutch, each resilient means comprising a stack of two or more belleville washers with a portion of the outermost washer of the stack protruding from the recess when the clutch is disengaged for contact with a second component of the clutch to provide the cushioning, characterised in that each stack of washers is located on the first component by a respective fastener which determines the axial position of the washers in the recess such that with the clutch disengaged the portion of the outermost washer protrudes from the recess by a predetermined amount.
A friction clutch in accordance with the second aspect advantageously provides axial cushioning with a minimum of moving parts whilst positively retaining the resilient means on the first component in a manner which simplifies assembly of the clutch and which can enable adjustment of the cushioning characteristics. In particular the arrangement has no relatively sliding components which may be liable to stick in use.
According to a third aspect of the invention, there is provided a friction clutch having means to cushion engagement of the clutch, the cushioning means comprising a plurality of circumferentially spaced resilient means located in one or more recesses in a first component of the clutch and arranged to bias a second component of the clutch axially away from the first to provide the cushioning, characterised in that each resilient means is held in its recess by a fastener carrying an axial abutment means for co-operation with its respective resilient means, the position of the axial abutment means relative to the base of the recess being determined by engagement of a stop on the fastener with corresponding stop on the first component such that when the stop on the fastener is fully tightened against the stop on the first component, the resilient means provides a predetermined cushioning pre-load.
This aspect of the invention advantageously provides for a simplified assembly of the friction clutch wherein the fasteners which locate the resilient means are fully tightened until the stop on the fastener engages with the stop on the first component. This ensures that the position of the axial abutment means on the fastener relative to the base of the recess or the resilient means is the same for each resilient means and so ensures that each resilient means is subjected to the same degree of compression without the need for the mechanic to carefully monitor the position of the axial abutment means relative to the base of the recess or the resilient means.
In a preferred embodiment, each resilient means in a clutch according to the third aspect may comprise a stack of two or more belleville washers in accordance with the second aspect. This provides a combination of the advantages of both the second and third aspects.
Further advantageous arrangements are defined in the various dependent claims.